Why is it that some shampoos sting our eyes? This is because shampoos are not like the tears in our eyes. In the case of shampoo, our eyes feel the difference right away. They send a 'stinging' message to our brain: Help! Something strange is here! To get rid of the strange substance, the brain tells our eyes to make more tears and wash the shampoo away. Some shampoos are specially made to be as much like the water in our eyes as possible. These 'tearless' shampoos fool our eyes and do not sting. Why does our skin become dry during winter? SILLY PIG The skin is composed of two main layers of cells: a thin outer layer, the epidermis, and a thicker inner layer, the dermis. The epidermis has no blood vessels. Its deeper strata contain melanin, the pigment that gives colour to the skin. The underlying dermis consists of connective tissue, with embedded blood vessels, lymph channels, nerve endings, sweat glands, fat cells, hair follicles and muscles. The skin is lubricated by its own oil glands, which keep the outside layer of the epidermis from drying to brittleness. However, in the harsh winter, the lubrication is inadequate because the air is cold and dry, so the skin feels dry and we have to use moisturising lotions. Our skin is very sensitive to heat and cold. Who invented the decimal point? While it is often thought of as a modern invention, the decimal point has been with us for around 400 years. Scottish mathematician John Napier (1550-1617) introduced the use of the decimal point in calculations. He was also responsible for that other bane of student life, logarithms. The decimal system itself is believed to have come into common use because humans have 10 fingers or digits (digit comes from the Latin for finger, digitus ). However, there are some societies which use toes or even parts of the arm to count to 20 and beyond. The modern system of writing 'Arab' numbers, such as 1999, only became widespread in Europe during the 13th century. The Roman system, which was in use until then, was proving too slow and cumbersome and lacked a zero. In Roman numerals, I was 1, V was 5, X was 10, L was 50, C was 100, D was 500 and M was 1,000. While 3 was written III, 4 was IV; 90 was XL and XXIV was 24. Easy? The introduction of the decimal system speeded up maths and made it much simpler to read. Why is it that dogs sniff everything? Sniffing is a dog's way of checking things out. A dog's nose can smell things about 40 times better than your nose can. By sniffing, a dog can tell who has been around its home recently. It can tell if there is another dog nearby, and if the animals it meets (and that includes you) are afraid or happy. A dog also sniffs to find food or hunt down an interesting-smelling animal, such as a rabbit or a cat.